HDD MACHINE WITH LOWERED DRIVELINE

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to co-pending U.S. Provisional Ser. No. 63/688,068 , filed Aug. 28, 2024, the entire contents of which are incorporated by reference herein.

BACKGROUND

The present invention relates to horizontal directional drilling (HDD) machines, and more particularly to the physical layout and sizing of fundamental mechanical elements thereof.

SUMMARY

In one aspect, the invention provides a horizontal directional drilling machine including a drilling frame defining a drilling frame longitudinal axis. A rack gear is mounted on the drilling frame, the rack gear having a pitch plane parallel to the longitudinal axis. A carriage assembly includes a carriage frame extending over the rack gear while being mounted with a linear bearing assembly for longitudinal movement along carriage guide surfaces of the drilling frame. A thrust drive motor is mounted on the carriage frame with no portion of the thrust drive motor extending laterally outboard of the carriage assembly. The thrust drive motor has an output shaft with a pinion gear meshed with the rack gear to define a carriage positioning axis as the longitudinal array of points of contact between the pinion gear and the rack gear that are nearest the thrust drive motor. A rotary drive assembly is mounted on the carriage frame, the rotary drive assembly having a drive spindle configured to engage a drill string for rotation about a longitudinal central rotation axis of the drive spindle, the drive spindle having an outer diameter. The central rotation axis of the drive spindle is offset from the carriage positioning axis by an offset distance equal to or less than 1.5 times the outer diameter of the drive spindle.

In another aspect the invention provides a horizontal directional drilling machine including a drilling frame defining a drilling frame longitudinal axis. A carriage assembly includes a carriage frame extending over the drilling frame while being mounted with a linear bearing assembly for longitudinal movement along the drilling frame, the carriage frame having a thrust drive support portion and a rotary drive support portion. A rotary drive assembly is mounted on the carriage frame, the rotary drive assembly having a drive spindle configured to engage a drill string for rotation about a longitudinal central rotation axis of the drive spindle. A longitudinal positioning system includes a thrust drive motor mounted on the carriage frame and is operable to move the carriage assembly along the longitudinal axis via a mechanical drive mechanism spaced below the central rotation axis of the drive spindle. The carriage frame includes a pair of sliding supports supporting the rotary drive assembly by engagement with a rotary drive housing thereof at positions that laterally flank the drive spindle. The central rotation axis of the drive spindle is positioned no higher than a reference line connecting respective centers of the pair of sliding supports.

Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial side view of an exemplar HDD machine, without the engine enclosure or operator station, in a view that will herein be referred to as from the right side, configured in accordance with the present application.

FIG. 2 is a partial side view of an exemplar HDD machine, without the engine enclosure or operator station, in a view that will herein be referred to as from the left side, configured in accordance with the present application.

FIG. 3 is a simplified side view of the exemplar HDD machine from the left side, showing the basic components separated.

FIG. 4 is a simplified side view of the exemplar HDD machine similar to FIG. 3, showing the main components in their typical positions with a drill head assembly in a position at which it is typically initially installed or mounted to the HDD machine.

FIG. 5 is a simplified side view of the exemplar HDD machine with the drill string pulled back as far as possible, until an enlarged section of the drill head enters the downhole vise, and with the rack tilted to a typical drilling position to start forming a bore hole.

FIG. 6 is a simplified cross-section taken along the line 6-6 as labelled in FIG. 5, showing the carriage assembly, rack assembly, rod loader. The rod loader is not included in FIG. 5. This cross-section illustrates components that are shown in the HDD machine of FIGS. 1 and 2.

FIG. 7 is a side view of the basic components of the carriage assembly as partially separated.

FIG. 8 is a front view of the basic components of the carriage assembly separated.

FIG. 8A is a front view of a carriage assembly including a gearbox housing according to one alternative construction.

FIG. 9 is a side view of the carriage assembly with force vectors illustrating forces that would be applied to the assembly during pullback.

FIG. 10 is a top view of the carriage assembly.

FIG. 11 is a cross-sectional view through line 11-11 illustrated on FIG. 10 showing the pinion gear engaged with the rack gear and labelling the carriage positioning anchor point.

FIG. 12 is a simplified side view of the exemplar HDD machine with the first section of the drill string, with one drill rod and the drill head, pushed forward to the position where it is secured by the downhole vise, with the rotary drive unthreaded, and moved back by the carriage to a position where a new drill rod can be inserted into the drill string.

FIG. 13 is a partial cross-section through the HDD machine at the line 13-13 illustrated on FIG. 12.

FIG. 14 is a partial cross-section through the HDD machine at the line 14-14 illustrated on FIG. 12.

FIG. 15 is a partial cross-section through the HDD machine at the line 15-15 illustrated on FIG. 5.

FIG. 16 is a partial cross-section through the HDD machine at the line 16-16 illustrated on FIG. 5.

FIG. 17 is a simplified side view of the exemplar HDD machine with the drill string pulled back as far as possible, until an enlarged section of the drill head enters the downhole vise, and with the rack tilted, and the back of the chassis raised to an alternative drilling position, to start forming a bore hole.

FIG. 18 is a simplified side view of an alternative embodiment HDD machine with the drill string pulled back as far as possible, until an enlarged section of the drill head enters the downhole vise, and with the rack tilted to a typical drilling position to start forming a bore hole.

FIG. 19 is a simplified side view of the alternative embodiment HDD machine with the first section of the drill string, with one drill rod and the drill head, pushed forward to the position where it is secured by the downhole vise, with the rotary drive unthreaded, and moved back by the carriage to a position where a new drill rod can be inserted into the drill string.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

FIGS. 1 and 2 illustrate an HDD machine 100 having a machine chassis 10 that is supported on ground engaging tracks 20. The chassis 10 supports a rack assembly 160. A rod box 30 is mounted to the rack assembly 160. The HDD machine 100 can also have an engine mounted in an engine enclosure, along with associated drive components such as hydraulic pumps and motors, although not shown in FIGS. 1 and 2. The HDD machine can also include an operator console or cab. The figures do not show the details of the engine, engine enclosure, or operator controls, in order to simplify the illustrations.

FIG. 3 is a simplified side view of the HDD machine 100, showing several components separated in order to clearly show the various components including the machine chassis 10, the ground engaging tracks 20, the rack assembly 160 including a rack foot 161 at a forward end thereof, a carriage assembly 110, a vise assembly 180, and a stake down assembly 190. The stake down assembly 190 is forward of the rack foot 161 and mounted to a forward end of the rack foot 161. This HDD machine 100 is configured to manipulate individual drill rods 32, that are connected to a drill head assembly 150. The drill head assembly 150 can include a drill head 152 and a starter or transition rod 154 positioned between the first drill rod 32 and the drill head 152. Drill bits 156 of various types can be mounted to the drill head 152. For a drill rod on the machine 100, a drill string axis is defined by a central rotation axis A of a drive spindle 140 of the carriage assembly 110.

FIG. 4 illustrates the rack assembly 160 connected at rack pivot 12 to the machine chassis. Rack pivot cylinder 14 is mounted to the chassis and connected to the rack assembly 160. The carriage assembly 110 is shown as mounted to the rack assembly 160 and positioned on one end, with the vise assembly 180 and the stake down assembly 190 at the opposite end. FIG. 5 illustrates the rack assembly 160 tilted down, as is controlled by the cylinder 14. More particularly, FIG. 5 illustrates the rack assembly 160 tilted down until first contact of the rack foot 161 with the ground. The rack foot 161 includes a flat bottom surface 161A that, once the rack assembly 160 is sufficiently tilted with respect to a horizontal ground plane 50, will lie along the horizontal ground plane 50 to establish a horizontal contact area therewith. In some constructions, the angle at which the rack foot 161 establishes flat contact along the ground plane 50 is 10-15 degrees (e.g., about 13 degrees) of downward rack angle from horizontal. The orientation shown in FIG. 5 can be the minimum drilling angle for the HDD machine 100, and it may be the transport or trailering orientation as the rack foot 161 can include tie-down anchors. The drill head assembly 150 is shown attached to or connected to a down hole end of the first drill rod 32. The drill rod 32 is connected at its uphole end to the drive spindle 140 of the rotary drive assembly 130 that is a component of the carriage assembly 110. In this configuration the carriage assembly 110 is positioned uphole along the rack assembly 160 to a maximally retracted position. Even with maximum retraction of the carriage assembly 110, the drill head 152 remains forward of the vise assembly 180. FIG. 5 illustrates a drill head 152 of typical length, and this results in a projecting length L of the drill string (in this case, just the drill head assembly 150 thereof) forward of the stake down assembly 190. The projecting length L can be 15 inches or less in some constructions (e.g., more particularly 12 inches or less in some constructions). With the drill head of this length on the HDD machine 100, a distal portion of the drill head 152 and the drill bit 156 are below the plane 50 of the ground surface that supports the ground engaging tracks 20 (which have a co-planar ground support portion). The plane 50 generally represents the local ground surface supporting the HDD machine 100, which may in fact be horizontal or oriented at a non-zero angle with respect to horizontal. The machine configuration in which the drill head 152 is at least partially below the ground plane 50 is the result of arranging several systems as will be described in more detail below.

FIG. 6 is a cross-section through the HDD machine 100 illustrating the general arrangement with a rack assembly 160 having a drilling frame or rack frame 162 including or configured as a U-shaped base member 164 (e.g., constructed from a rectangular tube or bent plate) and a top plate 166 secured together, such as by being welded. A rack gear 168 is secured to the drilling frame 162, for example connected by removeable fasteners. The carriage assembly 110 is movably mounted to the drilling frame 162, as will be shown in more detail in subsequent figures. The rod box 30, along with the rod loader arms 200 and a rod loader arm drive gear 201, are mounted to the drilling frame 162. The engine enclosure 102 is typically mounted on the chassis 10, positioned on the opposite side of the drilling frame 162. This figure illustrates the main components that affect the overall width of the machine 100. The width of the engine enclosure 102 is dictated by the physical size of the engine, and the associated cooling components, such as the radiator, and cooling fan. The width of the rod box 30 is dictated by the number of drill rods to be carried. The carriage assembly 110 and rack assembly 160 are positioned between the engine enclosure 102 and the rod box 30. The overall machine width is generally the sum of the width of these three, and the required clearances between these assemblies. For smaller HDD machines, which may need to be trailered with or without other components, such as a mix system for the supply of drilling fluid, overall machine width is an important criterion. As such, the width of the each of these components/systems is important. An optional operator cab is not included in the overall width described above. The HDD machine 100 can be limited to 55.5 inches or less for trailering to/from work sites on a standard double-axle trailer.

FIGS. 7 and 8 illustrate the arrangement of the carriage assembly 110, as configured to minimize its width. The rotary drive 130 is shown separated from the rest of the carriage assembly 110 in order to more clearly illustrate specific features of the components. The carriage assembly 110 is configured to be propelled along the drilling frame 162 by a thrust motor 124. The illustrated embodiment has two thrust motors 124. The thrust motors 124 are mounted to a first support surface 111 (e.g., top surface or top plate) of a carriage frame 112. As illustrated in FIGS. 10 and 11, an output shaft 125 of each thrust motor 124 is provided with a thrust pinion gear 126 (e.g., mounted to the output shaft 125 or integral with the output shaft 125). Each thrust pinion gear 126 is engaged (i.e., meshed) with the rack gear 168 of the rack assembly 160. The rack gear 168 is mounted to a planar mounting surface 170 on a portion of the top plate 166. The rack pitch line 169 is generally perpendicular to the planar mounting surface (e.g., top surface), and oriented in a general vertical orientation in order to reduce the potential for materials to set on the rack gear. The elongated rack gear 168 with its pitch line 169 defines a pitch plane. As the thrust pinion gear 126 is rotated by the thrust motor 124, the carriage assembly 110 moves in this plane, and along the longitudinal axis of the drilling frame 162.

The top plate 166 also has carriage guide surfaces 172, 173 (FIG. 11). In the illustrated embodiment, the carriage guide surfaces 172, 173 are at the laterally outer ends of the top plate 166 and include upper carriage guide surfaces 172 and lower carriage guide surfaces 173. The carriage frame 112 includes upper carriage supports 114 mounted in an upper plane and lower carriage supports 116 mounted in a lower plane. The upper and lower carriage supports 114, 116 are secured in position on the carriage frame 112 so that they engage with the carriage guide surfaces 172, 173, respectively, to hold the carriage assembly 110 to the drilling frame 162, while allowing it to move along the longitudinal axis of the drilling frame 162. The various supports form a linear bearing between the carriage frame 112 and the drilling frame 162 for supporting the longitudinal movement of the carriage assembly 110 along the drilling frame 162. In the illustrated construction, the upper carriage supports 114 are provided as rollers, and the lower carriage supports 116 are provided not as rolling elements but sliding elements, referred to as wear pads or blocks. However, support can be provided by any suitable combination of rollers and/or wear pads. An upper or lower carriage support 114, 116 can have a monolithic or composite polymer construction.

Side supports 230 (e.g., rollers) are mounted to the carriage frame 112 and positioned to engage with the back (non-toothed) side of the rack gear 168. These supports 230 hold the carriage assembly 110 in a position to ensure that the thrust pinion gear(s) 126 are properly engaged with the rack gear 168. As illustrated in FIG. 11, the thrust pinion gear 126 is mated with the rack gear 168. As viewed along the length of the rack gear 168 parallel to the drive spindle axis A, a point of contact between the rack gear 168 and the pinion gear 126 that is closest to the thrust motor 124 defines a carriage positioning anchor point 174 (FIGS. 6 and 11). As the carriage assembly 110 is propelled along the drilling frame 162, the anchor points 174 move along the drilling frame 162 to define a carriage positioning axis 176. In the illustrated embodiment this axis 176 is defined by this first or upper point of contact between the pinion gears 126 and the rack gear 168. Accordingly, the carriage positioning anchor point 174 and the carriage positioning axis 176 may be at or near the top edge of the rack gear 168. In other embodiments, the carriage positioning system may include alternate forms of mechanical drive mechanisms, including for example chains, or cylinders. These alternative embodiments also have a carriage positioning axis. For embodiments with a chain, that carriage positioning axis is the point, closest to the thrust motor 124, where a carriage drive sprocket contacts the chain. For embodiments with a cylinder, the carriage positioning axis is the point, closest to the thrust motor 124, where the cylinder contacts the carriage.

In addition to being configured to be movably mounted to the drilling frame 162, the carriage frame 112 is also configured to support the rotary drive assembly 130 with a rotary drive support 118 in the form of a pair of shafts 220 that are mounted in a front cross member 222 and rear cross member 224. The shafts 220 extend through corresponding apertures 144 in the rotary drive housing 142 (FIG. 8) to form a pair of sliding supports. The sliding supports for the rotary drive support 118 laterally flank the drive spindle 140. The spindle axis A is positioned no higher than a reference line R connecting respective centers of the pair of sliding supports (e.g., the centers of the shafts 220 and the corresponding apertures 144 in the illustrated embodiment). The rotary drive assembly 130, in the embodiment illustrated in FIG. 7, includes two rotary drive motors 132. Other embodiments may have more or fewer motors. The rotary drive motors 132 can be hydraulic motors, but can alternately be electric motors in other embodiments. The rotary drive motors 132 are mounted to the rotary drive housing 142, with a rotary drive pinon gear 134 provided on the output shaft of the motor(s) 132. An idler gear 136 is supported within the rotary drive housing 142, in mesh with the rotary drive pinion 134 and in mesh with a rotary drive final gear 138. This gear train is configured to provide an appropriate speed reduction, while also minimizing the overall width of the rotary drive housing 142, by vertically stacking the gears 134, 136, 138. A portion of the drive spindle 140 is mounted in the rotary drive housing 142 and is fixed to the rotary drive final gear 138 to rotate therewith. In other words, the drive spindle 140 is coaxial with the rotary drive final gear 138. The remainder of the drive spindle 140 extends out from the rotary drive housing 142, including a distal end operable to connect with the drill string during use of the HDD machine 100.

This arrangement of the carriage assembly 110 is configured, as previously described, to minimize a distance between the central axis A of the drive spindle 140 and the carriage positioning axis 176 (FIG. 9) that passes through the carriage positioning anchor point 174. This distance is referred to as the drill string or “driveline” offset X, labeled in FIGS. 6 and 9. The carriage positioning anchor point 174 and the carriage positioning axis 176 can be positioned at or near a top edge of the rack gear 168 in a construction where thrust drive is provided through a rack gear 168). A bottom-most portion of the rotary drive housing 142 can be at or below the carriage positioning anchor point 174 and the carriage positioning axis 176 in some constructions. In one possible construction, shown in detail in the front view of FIG. 8A, the rotary drive housing 142A may have a bottom edge 143 extending between the sliding supports, and the bottom edge 143 is provided by multiple separate profiles (e.g., separate curves or arcs). The separate profiles at the bottom edge 143 meet at a shoulder 145. The shoulder 145 is positioned such that the change in profile reduces the outside dimension (e.g., as measured from the drive spindle axis A) of the rotary drive housing 142A in the area closest to the carriage positioning anchor point 174 and the carriage positioning axis 176 (e.g., along the top of the rack gear 168). A bottom-most point of the bottom edge 143 can be at or below the carriage positioning anchor point 174 and the carriage positioning axis 176. Thus, a horizontal reference line extending transversely across the carriage assembly 110 (left-to-right in FIG. 8A) at the height of the carriage positioning anchor point 174 and the carriage positioning axis 176 may intersect the bottom edge 143 of the rotary drive housing 142A.

As depicted in FIG. 8A by the dashed line representing the inside wall surface of the rotary drive housing 142A, the separate profiles in the bottom edge 143 may result in a reduction in wall thickness of the rotary drive housing 142A from a first thickness T1 to a second thickness T2. Further adding to the vertical compactness, FIG. 8A illustrates that the base member 164A of the drilling frame 162 can be provided as a hollow rectangular member having a cross-section with a long side oriented horizontally and a short side oriented vertically. The base member 164A may be about twice as wide as it is tall. This may be similar to the U-shaped base member 164 of the other FIG.

Force vectors in FIG. 9 illustrate the forces that are applied to the carriage assembly 110 during a pullback operation. In this operation, the thrust/pullback motors 124 are powered to rotate the thrust pinion gears 126. Being engaged with the rack gear 168 (removed for clarity in FIG. 9), the rotation of the thrust pinion gear 126 results in generation of a carriage propulsion force 300. The carriage propulsion force 300 is in a direction determined by the direction of rotation of the thrust pinion gears 126. Although each thrust pinion gear 126 generates a separate carriage propulsion force, the illustration is simplified such that the force vector 300 represents the combined force. The combined carriage propulsion force 300 acts at the center of the height of the thrust pinion gears 126 as shown in FIG. 9. The placement of the carriage propulsion force 300 at this height can be considered an average or an approximation, as the actual pressure distribution between the teeth of the rack gear 168 and the pinions 126 may fluctuate during operation within a machine, or from one machine to another. The pullback force vector 310 illustrates the force that the drill string exerts on the drive spindle 140, as it resists movement in the direction of the carriage propulsion force 300. In general, the pullback force 310 will be equivalent to the carriage propulsion force 300. There are frictional forces acting on the carriage assembly 110, but for the purposes of this disclosure, frictional forces are not accounted for in this simplified load model. The connection between the thrust motors 124 and the drilling frame 162 being offset below the spindle axis A creates a moment or torque acting on the carriage assembly 110, which in turn results in a force 320 acting on the front upper carriage support 114 and a force 330 acting on the rear lower carriage support 116. FIG. 6 illustrates the outer diameter D of the drive spindle 140 and how the related parts are positioned closely together including the rod loader arm 200, the rack gear 168, and the drive spindle 140. The ratio X:D of the driveline offset X to the outer diameter D of the drive spindle 140 can be 1.5:1 or less. In some constructions, the ratio X:D of the driveline offset X to the outer diameter D of the drive spindle 140 can be 1.35:1 or less (e.g., 1.26:1). Reducing the offset X and the X:D ratio results in reduced forces 320, 330 and reduced loads induced on the carriage guides 172 during operation.

FIG. 12 illustrates a condition where the drill string consisting of a first drill rod 40 and drill head assembly 150 are pushed into the ground, by moving the carriage assembly 110 along the drilling frame 162 to the down hole end where the joint between the drive spindle 140 and the first drill rod 40 is positioned between a downhole vise 182 and an uphole vise 184. The downhole vise 182 has clamped the first drill rod 40 in this figure. The rotary drive assembly 130 has already reverse-rotated the drive spindle 140 to separate from the first drill rod 40, and the carriage assembly 110 has been propelled back up the drilling frame 162 to an upward or rearward end to make room for a second drill rod 42. As shown, the second drill rod 42 is staged for connection to the drill string and subsequent extension of the bored hole.

FIGS. 13 and 14 illustrate a rod storage and transfer system utilized for staging the second drill rod 42 (and each subsequent drill rod). FIG. 13 is a cross-section taken along the drilling frame 162 at the position indicated by the line 13-13 shown in FIG. 12. A rod lifting assembly 210 operable to vertically lift drill rods into the rod box 30 is positioned underneath the rod storage box 30 at this location. In this embodiment, the rod storage box 30 is positioned so that the bottom of the rod box is at a plane at the same elevation as the top of the staged drill rod 42. At this staged location the axis of the drill rod 42 is co-axial with the axis A of the drive spindle. The center of the staged drill rod 42 is offset from the carriage positioning axis 176 by the drill string offset X. In comparison with conventional HDD machines, reduction of the drill string offset X thus allows the rod box 30—and the entirety of its contents—to be lowered. In other words, if the drill string offset X was increased, the rod box 30 would need to be higher, for an HDD machine with a rod storage and transfer system of this type.

FIG. 14 illustrates the rod transfer assembly 206 with a rod loader arm 200 having a rod seat 202 configured to hold a drill rod as it is moved into the rod staging location. The rod loader arm 200 has an upper surface 204 that blocks off the individual rows of rods that may be stored in the rod box 30. This upper surface 204 is aligned with the bottom of the rod box 30. The rod transfer assembly 206 can include a rack and pinion mechanism (e.g., the rack formed on the rod loader arm 200) as shown in FIGS. 6 and 14.

As illustrated in FIG. 13, the rod lifting assembly 210 includes a rod lift cylinder 212 with a bottom end 214 that is positioned proximate the ground surface 50. In the embodiment of FIG. 12, the rod lifting assembly 210 that is situated at a longitudinal position (along the length of the drilling frame 162), closest to the downhole end of the drilling frame 162, is positioned such that the bottom end 214 of the rod lift cylinder 212 does not contact the ground. This position of the downhole rod lifting assembly 210 is rearward or uphole from the downhole rod transfer assembly 206 (detailed in FIG. 14).

As illustrated in FIG. 12, the HDD machine 100 places the rod transfer assembly 206 closest to the down hole or front end of the drill rod 42 that is being transferred into alignment with the drill string. The rod lifter assembly 210 is positioned slightly uphole or rearward of the rod transfer assembly 206, in order to provide for clearance with the ground. At the opposite end of the drill rod 42, a second rod lifter assembly 210 is positioned closest to the uphole end of the drill rod 42, while a second rod transfer assembly 206 is positioned slightly downhole from the adjacent rod lifter assembly 210. In this embodiment the rod storage and transfer system can be described as being arranged in an order along the drill rod 42, from the downhole end to the uphole end, as transfer-lifter-transfer-lifter.

FIGS. 18 and 19 illustrate an HDD machine 500 of an alternative construction where the drilling frame 162 and carriage 110 are configured to provide the same drill string offset X as described for the HDD machine 100 of the preceding embodiment, but wherein the drilling frame 162 is designed to place the rack gear 168 at a raised position, as compared to the embodiment of FIGS. 5 and 12. With the alternative embodiment 500 of FIG. 18, the drill string is high enough that the downhole rod lifter assembly 210 can be positioned closest to the downhole end of the drill rod (i.e., closer than the adjacent rod transfer assembly 206). This is possible due to the fact that the drill string is higher, so that there is adequate clearance to the ground plane 50 at that location. In this arrangement the rod storage and transfer system can be described as being arranged in an order along the drill rod, from the downhole end to the up hole end, as lifter-transfer-transfer-lifter. With this alternative embodiment, as shown in FIG. 18, the drill head 150 and drill bit 156 (projecting the length L forward of the stake down assembly 190) do not interfere with the ground surface 50 as the drilling rack is set down into the orientation illustrated in FIG. 18, which corresponds to that of FIG. 5 where the rack foot bottom surface 161A lies flat on the ground. This is because, although the drill string offset X is small, the drive spindle axis A is not lowered within the machine as in the machine 100 of FIG. 5.

In contrast, the HDD machine 100 of FIG. 5 places the projected portion of the drill string in interference with the ground surface 50 when first set down into a normal drilling position (i.e., when the rack foot bottom surface 161A lies flat on the ground). Lowering of the drill string offset X of this embodiment is achieved by lowering the drive spindle axis A within the HDD machine 100, which provides a benefit for the overall machine balance. As illustrated in FIG. 13, the height of a center of gravity 60 of a full rod box 30 is directly affected by the height of the drill string, which is set by the height of the drive spindle axis A. By lowering the drive spindle axis A within the machine 100 shown in FIGS. 5 and 12, the stability of the machine 100 has been found to be improved.

Lowering of the drive spindle axis A not only affects the arrangement of the rod storage and transfer mechanism, but also of the vise assembly 180. FIG. 15 illustrates the basic arrangement of the downhole vise 182 in a cross-section view along line 15-15 of FIG. 5 with a vise clamp cylinder 380, an upper vise die 382 and a bottom vise die 384. With the height of the drill string in this lowered position, the bottom vise die 384 is located close to the ground plane 50.

FIG. 16 illustrates the uphole vise assembly 184 in a cross-section view along line 16-16 of FIG. 5 with a vise clamp cylinder 390, an upper vise die 392 and a bottom vise die 394. The vise clamp cylinder 3990 and vise dies 392, 394 are mounted on a second frame 398 that is rotatably mounted on a first frame 396. The second frame 398 is able to rotate relative to the first frame 396 about a breakout vise axis 402 that is positioned to be co-axial with the drill string axis A. A variety of arrangements of these frames are known, thus the details are not described herein. A breakout cylinder 400 is connected to both the first frame and the second frame, to allow the second frame 398, vise clamp cylinder 390 and vise dies 392 and 384 to rotate in order to generate torque required to break a joint in the drill rods that is positioned between the downhole vise 182 and the uphole vise 184. With the height of the drill string in this lowered position, the breakout cylinder 400 is located close to the ground plane 50.

FIG. 17 is an illustration of the HDD machine 100 in an elevated orientation where an outrigger assembly 80 has been deployed to raise the uphole end of the machine. In this configuration, the drill head assembly 150 and drill bit 156 are further below the ground plane 50 than when in the condition shown in FIG. 5. Both drawings illustrate the drill string prior to forward thrust of the drill string by the carriage assembly 110.